Fractional Frequency Reuse (FFR) and Soft Frequency Reuse (SFR) are techniques used for inter-cell interference mitigation in networks such as Orthogonal Frequency-Division Multiple Access (OFDMA) networks. In both techniques the numbers of allocated channels or subcarriers or resource blocks for cell-edge (CEUs) and cell-centre users (CCUs) are independently predetermined for every adjacent cell. Each cell then assigns a different subset of channels to their cell-edge users. This is to ensure that the given channels will not overlap among adjacent cells. This principle is used to avoid inter-cell interference.
In FFR the channels allocated for cell edge users in a given cell are reserved, that is the channels are barred from use by neighbouring cells. This results in low spectrum efficiency as a trade-off to achieve better cell-edge performance since in any given cell some resources are prevented from being used.
In SFR, different subcarrier power levels are used for CCUs and CEUs. A low power is used to transmit signals to CCUs and a high power is used to transmit signals to CEUs. The reason for this is that it is the CEUs that mostly experience high interference, so a high subcarrier power is required to mitigate the interference. For CCUs a low subcarrier power is sufficient. SFR utilises all resources of the network in each cell. This results in high spectrum efficiency.